082
FXUS02 KWBC 181906
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
306 PM EDT SUN MAY 18 2025
VALID 12Z WED MAY 21 2025 - 12Z SUN MAY 25 2025
..OVERVIEW
AN UPPER LOW DEVELOPS AND STALLS OVER THE GREAT LAKES WEDNESDAY AND
THURSDAY BEFORE SLOWLY TRACKING OVER THE NORTHEAST FRIDAY INTO
SATURDAY, PROMOTING COOLER TEMPERATURES. ASSOCIATED SURFACE LOW
PRESSURE WILL LINGER OVER THE OHIO VALLEY WEDNESDAY BEFORE ENERGY
IS TRANSLATED TO A NEW COASTAL LOW TRACKING ALONG THE MID-ATLANTIC
WEDNESDAY NIGHT THROUGH THURSDAY AND NEW ENGLAND THURSDAY NIGHT AND
FRIDAY BEFORE STALLING OVER ATLANTIC CANADA, WITH RAIN AND
THUNDERSTORMS IN THE VICINITY OF THE LOW. UPSTREAM, AN UPPER RIDGE
DRIFTS FROM THE SOUTHWESTERN U.S. TO THE SOUTHERN PLAINS WEDNESDAY
THROUGH FRIDAY, LEADING TO ABOVE AVERAGE TEMPERATURES IN THOSE
AREAS.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE REMAINS IN RATHER GOOD AGREEMENT WITH SHORTWAVE
ENERGY OVER THE MIDWEST WEDNESDAY DEVELOPING INTO A STALLED LOW
OVER THE NORTHERN GREAT LAKES THROUGH THURSDAY. THE ASSOCIATED
SURFACE LOW, PARTICULARLY THE COASTAL LOW THAT SLOWLY MOVES UP THE
EASTERN SEABOARD CONTINUES TO HAVE SOME DIFFERENCE IN GUIDANCE WITH
THE GFS REMAINING THE MOST PROGRESSIVE. AGREEMENT ALSO REMAINS WITH
THE SOUTHWEST UPPER RIDGE BUILDING AND SLOWLY MOVING EAST THROUGH
THE SOUTH-CENTRAL U.S. LATE WEEK.
FARTHER NORTH THERE IS MORE AGREEMENT ON SHORTWAVES COMING INTO THE
NORTHWEST WEDNESDAY NIGHT INTO FRIDAY AHEAD OF A MORE POTENT LOW
APPROACHING THE PACIFIC NORTHWEST ON FRIDAY. THE 12Z GFS IS MORE
OPEN WITH THIS POTENT WAVE/LOW AND ALLOWS IT TO DIG TO CALIFORNIA
WHILE THE EC/CMC KEEP IT NORTH.
THE WPC FORECAST WAS BASED ON A GENERAL BLEND OF DETERMINISTIC
MODELS THROUGH DAY 7 WITH ONLY INCLUSION OF ENSEMBLE MEANS FOR DAYS
6/7 WHEN THE UKMET IS NO LONGER AVAILABLE TO WPC. WPC QPF DAYS 4-7
ARE A BLEND OF THE 13Z NBM WITH THE 00Z EC ALONG WITH SOME 06Z
GFS AND 00Z CMC/UKMET WHERE APPROPRIATE.
..WEATHER/HAZARDS HIGHLIGHTS
WIDESPREAD RAIN WITH EMBEDDED HEAVIER THUNDERSTORMS ACROSS EASTERN
PORTIONS OF THE OHIO VALLEY, NORTH-CENTRAL APPALACHIANS AND MID-
ATLANTIC REGION ON WEDNESDAY WITH A SURFACE LOW TRACKING THROUGH.
A DAY 4 MARGINAL RISK ERO REMAINS IN PLACE FROM THE CENTRAL
APPALACHIANS THROUGH MUCH OF THE MID-ATLANTIC AND SOUTHERN NEW
YORK. AMPLE MOISTURE, BUT LIMITED INSTABILITY IN A COLD AIR DAMMING
WEDGE SHOULD LIMIT OVERALL RAINFALL POTENTIAL, THOUGH THE THREAT OF
REPEATING HEAVIER RAINS IS POSSIBLE AS THE LOW PIVOTS.
A NEW MARGINAL RISK ERO FOR DAY 4 IS RAISED FOR PORTIONS OF FAR
SOUTH TEXAS ALONG A FRONTAL BOUNDARY AND WILL MOVE INTO THIS AREA
WHICH HAS SEEN RECORD HIGH TEMPERATURES AND CONTINUED INFLUX OF
GULF MOISTURE (SO THERE IS PLENTY OF MOISTURE INSTABILITY).
THE DAY 5 MARGINAL RISK REMAINS FROM THE NYC METRO THROUGH SOUTHERN
AND CENTRAL NEW ENGLAND FOR RAINFALL WRAPPING AROUND THE COASTAL
LOW. COOLER TEMPERATURES WITH THE LOWER HEIGHTS ALOFT COULD
PRODUCE SOME MAY SNOW IN THE HIGHER PEAKS OF THE WHITE MOUNTAINS
WITH THIS SYSTEM. RAIN LINGERS IN THE NORTHEAST THROUGH FRIDAY AS
THE LOW PULLS AWAY SLOWLY.
SOME ROUNDS OF RAIN ARE POSSIBLE IN MEAN NORTHWEST FLOW BEHIND THE
EASTERN UPPER TROUGH, AFFECTING THE NORTHERN PLAINS TO MIDWEST.
THE NORTHWEST MAY SEE PRECIPITATION WITH SHORTWAVES MOVING THROUGH.
MEANWHILE SOME CONVECTION IS LIKELY EAST OF A SOUTHERN HIGH PLAINS
DRYLINE. BY LATE WEEK INTO THE WEEKEND, SYSTEMS MAY COMBINE AND
PRODUCE BROADER AREAS OF HEAVIER RAIN IN THE CENTRAL U.S., BUT WITH
UNCERTAINTY IN THE DETAILS.
THE HEAT ACROSS TEXAS SHOULD ABATE SOMEWHAT BY WEDNESDAY AS UPPER
TROUGHING SUPPRESSES THE SUBTROPICAL RIDGE AND THE FRONTAL BOUNDARY
APPROACHES/MOVES THROUGH. THE TROUGH/LOW ALOFT WILL PROMOTE BELOW
NORMAL TEMPERATURES ACROSS THE NORTHERN TIER, WITH TEMPERATURES OF
15 TO 20 DEGREES BELOW AVERAGE IN THE NORTHERN PLAINS, ONLY
REACHING THE 50S ON WEDNESDAY. BROAD AREAS OF THE EAST-CENTRAL AND
EASTERN U.S. CAN EXPECT BELOW AVERAGE TEMPERATURES THROUGH THE
LATTER HALF OF NEXT WEEK AS THE UPPER TROUGH SETS UP.
MEANWHILE, UPPER RIDGING WILL RAISE TEMPERATURES ABOVE NORMAL OVER
THE SOUTHWEST. THE LOS ANGELES METRO IN PARTICULAR IS FORECAST TO
MEET DAILY RECORD HIGHS WITH THE ABOVE AVERAGE CONDITIONS IN
CALIFORNIA WEDNESDAY- THURSDAY. THE WARMTH WILL EXPAND EAST
ACROSS THE FOUR CORNERS STATES BY THURSDAY AND INTO THE SOUTHERN
PLAINS LATE IN THE WEEK. HIGHS WILL BE WELL INTO THE 100S IN THE
DESERT SOUTHWEST WITH TEMPERATURES NEARING 100 AGAIN IN PARTS OF
TEXAS EVENTUALLY.
JACKSON
ADDITIONAL 3-7 DAY HAZARD INFORMATION CAN BE FOUND ON THE WPC
MEDIUM RANGE HAZARDS OUTLOOK CHART AT:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
WPC MEDIUM RANGE 500MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,
QUANTITATIVE PRECIPITATION FORECAST (QPF), EXCESSIVE RAINFALL
OUTLOOK (ERO), WINTER WEATHER OUTLOOK (WWO) PROBABILITIES, HEAT
INDICES, AND KEY MESSAGES CAN BE ACCESSED FROM:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST500_WBG.GIF
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST_WBG_CONUS.GIF
HTTPS://WWW.WPC.NCEP.NOAA.GOV/5KM_GRIDS/5KM_GRIDSBODY.HTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/QPF/DAY4-7.SHTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=ERO
HTTPS://WWW.WPC.NCEP.NOAA.GOV/WWD/PWPF_D47/PWPF_MEDR.PHP?DAY=4
HTTPS://WWW.WPC.NCEP.NOAA.GOV/HEAT_INDEX.SHTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=OVW
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